Polyisobutylene Production Process With Improved Efficiencies And/Or For Forming Products Having Improved Characteristics And Polyisobutylene Products Produced Thereby

ABSTRACT

A process for production of polyisobutylene includes subjecting a reaction admixture comprising isobutylene, a diluent for the isobutylene, which may be isobutane, and a catalyst composition, that may include a BF 3 /methanol catalyst complex, to reaction conditions suitable for causing at least a portion of the isobutylene to undergo polymerization to form a polyisobutylene product including polyisobutylene molecules. At least a fraction of the polyisobutylene molecules thus produced have alpha position double bonds and the polyisobutylene product has a number average molecular weight (M N ) and a polydispersity index (PDI). The concentration of the diluent in the reaction admixture may be manipulated to control or change any one or more of (a) the relative size of the fraction, (b) the number average molecular weight of the product, (c) the polydispersity index of the product and (d) the relative size of the portion. The diluent concentration may be held constant to maintain any one or more of such characteristics constant.

CROSS REFERENCE TO RELATED APPLICATIONS

None

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention described hereinafter relates to improvements in thepolymerization of isobutylene. In particular the invention relates toprocesses for preparing polyisobutylene (PIB) products having improvedcharacteristics. More particularly, the invention relates to techniquesfor manipulation and control of liquid phase processes for producingpolyisobutylene, polyisobutylene products having pre-selectedcharacteristics, and methodology which enhances the operation andcontrol of polyisobutylene reactors.

2. Background of the Invention

U.S. Pat. No. 6,562,913 issued on May 13, 2003 and entitled “Process forProducing High Vinylidene Polyisobutylene” (hereinafter the '913 patent)relates, inter alia, to liquid phase polymerization processes forpreparing low molecular weight (number average molecular weight (M_(N))less than about 10,000), highly reactive (terminal double bond contentof at least about 70%) polyisobutylene products. In accordance with thedisclosure of the '913 patent, a catalyst composition, which desirablymay comprise a complex of BF₃ and complexing agent such as methanol, anda feedstock containing isobutylene, are each introduced into a reactionzone where the same are intimately admixed with residual reactionmixture so as to present an intimately intermixed reaction admixture inthe reaction zone. The intimately intermixed reaction admixture ismaintained in its intimately intermixed condition and at a relativelyconstant temperature of at least about 0° C. while the same is in thereaction zone, whereby isobutylene therein is polymerized to form apolyisobutylene product having a high degree of terminal (vinylidene)unsaturation. A crude product stream comprising residual catalystcomposition, unreacted isobutylene and polyisobutylene is then withdrawnfrom the reaction zone. The introduction of feedstock into and thewithdrawal of product stream from the reaction zone are each controlledsuch that the residence time of the isobutylene undergoingpolymerization in the reaction zone is no greater than about 4 minutes,whereby the product stream contains a highly reactive polyisobutyleneproduct. Preferably, the reaction zone may be the tube side of ashell-and-tube exchanger in which a coolant is circulated on the shellside. A recirculation loop may desirably be employed to circulate thereaction admixture through the tube side reaction zone at a linearvelocity sufficient to establish and maintain an intimately intermixedcondition in the admixture and remove heat generated by the exothermicpolymerization reaction.

U.S. Pat. No. 7,037,999 issued on May 2, 2006 and entitled “Mid-RangeVinylidene Content Polyisobutylene Polymer Product and Process forProducing the Same” (hereinafter the '999 patent) describes, inter alia,mid-range vinylidene content PIB polymer products and processes formaking the same. In accordance with the disclosure of the '999 patent,at least about 90% of the PIB molecules present in the product arepolyisobutylene isomers having either alpha or beta position doublebonds. The alpha (or terminal) position double bond (vinylidene) isomercontent of the product may range from 20% to 70% thereof, and thecontent of tetra-substituted internal double bonds is very low,preferably less than about 5% and ideally less than about 1-2%. Themid-range vinylidene content PIB polymer products are desirably preparedby a liquid phase polymerization process conducted in a loop reactorsimilar to the reactors described in the '913 patent at a temperaturewhich desirably may be about 60° F. or higher using a BF₃/methanolcatalyst complex and a contact time of no more than about 4 minutes.

U.S. Pat. No. 6,992,152 issued on Jan. 31, 2006 and entitled “Apparatusand Method for Controlling Olefin Polymerization process” (hereinafterthe '152 patent) relates, inter alia, to methodology for controlling theoperation of reactors such as those described in the '999 and '913patents so as to achieve efficiencies in process operation and betteruniformity of the product of the process. In particular, the '152 patentdescribes methodology for controlling the ratio of BF₃ to catalystcomposition to thereby control the reactivity (terminal double bondcontent) of the product. Specifically, such control is achieved byproviding for introduction of a catalyst modifier separately from theintroduction of the catalyst composition itself.

U.S. Pat. No. 6,844,401 issued on Jan. 18, 2005 and entitled “Apparatusfor Preparing Polyolefin Products and Methodology for Using the Same”(hereinafter the '401 patent) relates, inter alia, to procedures, etc.for improving the processes described above. In particular the '401patent describes an olefin reactor system that includes at least twoseparate reactor zones operating in parallel. Such multiple reactorsystem provides process efficiencies and advantages particularly inconnection with conversion rates and polymer polydispersity. Inaddition, the '401 patent describes downstream systems for quenching theresidual catalyst leaving with the crude product to quickly preventfurther reaction, for removal of catalyst residues by washing, and forseparation of the product from unreacted monomer, dimers, oligomers andother undesirable contaminants such as diluents and the like.

In accordance with certain of the preferred embodiments of the '913,'999, '152 and '401 patents, polyisobutylene products may bemanufactured by processes comprising liquid phase polymerizationconducted in a loop reactor at a temperature ranging from 30 to 90° F.The preferred catalyst may be a BF₃/methanol catalyst complex and thereactor residence time may usually be no more than about 4 minutes. Oneof the preferred products may be a relatively low molecular weight,mid-range (50-60%) alpha position (vinylidene) double bond content PIBpolymer. At least about 90% of the PIB molecules present in the productare either alpha position (vinylidene) double bond or beta positiondouble bond isomers. The other polyisobutylene isomers producedgenerally may comprise less than 10% and ideally less than 5% of themolecules.

Table 1 set forth below shows possible isomer structures that might befound in low molecular weight polyisobutylene products. Other isomersmay possibly be included in minor amounts and should not affect theoverall reactivity of the PIB molecule.

In general, the reactivity of an olefinic double bond is directlyrelated to its degree of substitution. That is to say, the more highlysubstituted the olefinic double bond, the less reactive it is.Therefore, since Structure I (alpha position or vinylidene double bond)of Table 1 is only disubstituted, it is much more reactive thanStructures II, III or IV where the double bond is in a beta position.Structures II and III are both 1,2,2 trisubstituted and are lessreactive than Structure I, but because there is an available hydrogen onthe terminal carbon, they are more reactive than Structure IV which is1,1,2-trisubstituted with no terminal hydrogen. Structure V istetra-substituted and is the least reactive of all the depicted isomers.

Generally speaking, PIB products produced in accordance with theprocesses described in the '913, '999, '152 and '401 patents discussedabove contain mainly Structures I and IV with the other isomers beingpresent in only minor concentrations. Highly reactive (HR)polyisobutylene products (see the '913 patent) may generally containabout 80-85 mole % of Structure I (alpha position double bond) and about15-20 mole % of Structure IV (beta position double bond). Mid-rangevinylidene content PIB polymer products (see the '999 patent), which maysometimes be referred to as “enhanced” products, also are generallypredominantly comprised of only Structures I and IV, but generally in aratio of about 55-60 mole % of Structure I and about 35-40 mole % ofStructure IV, respectively, with minor concentrations of the otheroligomers.

TABLE 1 Structures of PIB Isomers I

II

III

IV

V

The '913, '999, '152 and '401 patents discussed above are each assignedto the assignee of the present application, and the entireties of therespective disclosures thereof are specifically incorporated herein bythis reference thereto.

In conducting the processes described above, highly specializedequipment and procedures may often be utilized to enhance the operationand control of the polymerization reactions that are involved. Moreover,as in any industrial activity, methodology and/or equipment forenhancing capacity and throughput are sought continually. In particularit is often very important in production of polyisobutylene to be ableto carefully control (optimize) the rate at which the isobutylene isconverted to polyisobutylene (conversion rate). It is also highlyimportant in many cases to be able to carefully control (optimize) thepolydispersity index (PDI) and/or the number average molecular weight(M_(N)) of the polyisobutylene product. Even more importantly, it isextremely valuable in many commercial applications to be able tocarefully control the concentration of reactive (terminal) double bondsin the polyisobutylene product.

SUMMARY OF THE INVENTION

In accordance with the concepts and principles of the inventiondescribed herein, a process for production of polyisobutylene isprovided which addresses the issues presented in connection with priorart processes such as those described above. In particular, in one ofits several important aspects, the invention described herein provides apolyisobutylene production process that includes subjecting a reactionadmixture containing isobutylene, a diluent for the isobutylene and acatalyst composition to reaction conditions suitable for causing atleast a portion of the isobutylene to undergo polymerization to form apolyisobutylene product including polyisobutylene molecules The reactionconditions are preferably such that at least a fraction of thepolyisobutylene molecules thus produced have alpha position (vinylidene)double bonds and the polyisobutylene product has a number averagemolecular weight and a polydispersity index. The process of theinvention further includes the manipulation of the concentration of thediluent in the admixture to thereby control any one or more of (a) therelative size of the portion of the isobutylene that is converted topolyisobutylene, (b) the number average molecular weight of the product,(c) the polydispersity index of the product and (d) the relative size ofthe fraction of the polyisobutylene molecules thus produced that possessalpha position double bonds.

In further accordance with the concepts and principles of the invention,the diluent may preferably comprise isobutane and the catalystcomposition may comprise a complex of BF₃ and a primary alcoholcomplexing agent. Ideally, the complexing agent may be methanol.

In further accordance with the invention, the reaction admixture maypreferably be subjected to suitable reaction conditions in a reactionzone where the reaction admixture is maintained in an intimatelyintermixed condition. Ideally, the zone may comprise a loop reactorreaction zone.

In still further accordance with the concepts and principles of theinvention, it has been found that the relative size of the portion ofthe isobutylene that is converted to polyisobutylene is a directfunction of the diluent concentration, the polydispersity index of theproduct is an indirect function of the diluent concentration, theaverage molecular weight of the product is an indirect function of thediluent concentration, and the relative size of the fraction of theproduced polyisobutylene molecules having alpha position double bonds isa direct function of the diluent concentration. Thus, and again inaccordance with the concepts and principles of the invention, theconcentration of the diluent in the admixture may be increased tothereby increase the relative size of said fraction and/or said portion,the concentration of the diluent in the admixture may be increased tothereby decrease the polydispersity index of the product, and theconcentration of the diluent in the admixture may be decreased tothereby increase the average molecular weight of the product.

Desirably, the concentration of the diluent in the admixture should beno more than about 50 weight % and preferably. the concentration of thediluent in the admixture should be no more than about 30 weight %, andideally the concentration of the diluent in the admixture should be inthe range of from about 8 to about 15 weight %.

In further accord with the concepts and principles of the invention, aprocess is provided which may include the step of selecting a diluentconcentration for the admixture corresponding to a given relative sizeof said fraction, and the manipulating step may comprise maintaining thediluent content of the admixture at the selected concentration tothereby hold the relative size of said fraction essentially constant. Inaddition the process may include the step of selecting a diluentconcentration for the admixture corresponding to a given polydispersityindex level, and the manipulating step may comprise maintaining thediluent content of the admixture at the selected concentration tothereby hold the polydispersity index of the product essentiallyconstant. Also, the process may include the step of selecting a diluentconcentration for the admixture corresponding to a given relative sizeof said portion, and the manipulating step may comprise maintaining thediluent content of the admixture at the selected concentration tothereby hold the relative size of the portion essentially constant. Ofcourse, as would be readily understood by the routineer in the olefinpolymerization art, the specific numerical correspondence betweendiluent concentration and any one or more of polydispersity index,molecular weight, size of fraction and/or size of portion will oftenneed to be determined empirically in advance in order to have a set ofvalues from which to select a predetermined diluent concentration.Conversely, the content and/or characteristics of the product stream maysimply be monitored and the diluent concentration varied as needed inresponse.

In further accordance with the invention, the process may include thesteps of treating the product to remove diluent and unreactedisobutylene therefrom and recycling at least one of the diluent and theunreacted isobutylene back to the reaction zone.

Furthermore, the invention provides a process for production ofpolyisobutylene that comprises subjecting a reaction admixturecomprising isobutylene, a diluent for the isobutylene and a catalystcomposition to reaction conditions suitable for causing at least aportion of the isobutylene to undergo polymerization to form apolyisobutylene product including polyisobutylene molecules and whereinat least a fraction of the polyisobutylene molecules have alpha positiondouble bonds, said polyisobutylene product having a number averagemolecular weight and a polydispersity index, said polyisobutyleneproduct having at least one parameter that is variable as a function ofthe concentration of the diluent in the admixture, said at least oneparameter comprising (a) the relative size of said fraction, (b) thenumber average molecular weight of the product, (c) the polydispersityindex of the product or (d) the relative size of the portion. Inaccordance with this aspect of the invention, the process may includethe steps of choosing a diluent concentration corresponding to apre-selected value of said at least one parameter and then maintainingthe admixture at said chosen diluent concentration to thereby hold saidparameter at the pre-selected value. In further accordance with thisaspect of the invention, the parameter may comprises the relative sizeof said portion, the average molecular weight of the product, thepolydispersity index of the product and/or the relative size of saidfraction.

The invention further provides an improved process for production ofpolyisobutylene wherein a reaction admixture including isobutylene, adiluent for the isobutylene and a catalyst composition is subjected toreaction conditions suitable for causing at least a portion of theisobutylene to undergo polymerization to form a polyisobutylene productincluding polyisobutylene molecules, wherein at least a fraction of thepolyisobutylene molecules have alpha position double bonds and whereinthe polyisobutylene product has a number average molecular weight and apolydispersity index, the improvement comprising increasing theconcentration of the diluent in the admixture to thereby increase therelative size of said fraction, increase the relative size of saidportion, decrease the number average molecular weight of the product,and/or decrease the polydispersity index of the product.

Conversely the invention provides an improved process for production ofpolyisobutylene wherein a reaction admixture including isobutylene, adiluent for the isobutylene and a catalyst composition is subjected toreaction conditions suitable for causing at least a portion of theisobutylene to undergo polymerization to form a polyisobutylene productincluding polyisobutylene molecules, wherein at least a fraction of thepolyisobutylene molecules have alpha position double bonds and whereinthe polyisobutylene product has a number average molecular weight and apolydispersity index, the improvement comprising decreasing theconcentration of the diluent in the admixture to thereby decrease therelative size of said fraction, decrease the relative size of saidportion, increase the number average molecular weight of the product,and/or increase the polydispersity index of the product.

The invention further provides novel polyisobutylene products producedby the processes described above.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic diagram illustrating a laboratory reactorarrangement set-up for conducting isobutylene polymerization processesin accordance with the invention;

FIG. 2 is a graph showing the variation of polymer alpha (vinylidene)double bond content with changing diluent concentration (data at 40°F.);

FIG. 3 is a graph showing molecular weight (M_(N)) and polydispersityindex (PDI) trends with changing diluent concentration (data at 40° F.)(filled symbols show M_(N) values—left axis; unfilled symbols showPDI—right axis);

FIG. 4 is a graph showing conversion trends with changing diluentcontent;

FIG. 5 is a schematic diagram depicting a PIB production processequipped for continuous recycling of isobutylene and/or diluent;

FIG. 6 is a graph showing variations in M_(N) with changing diluent(isobutane) concentration;

FIG. 7 is a graph showing variations of viscosity (v) with changingdiluent (isobutane) concentration;

FIG. 8 is a graph showing variations of PDI with changing diluent(isobutane) concentration; and

FIG. 9 is a graph showing variations of alpha (vinylidene) double bondcontent with changing diluent (isobutane) concentration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The concepts and principles of the invention described herein aregenerally applicable in connection with each of the various PIB reactorsand PIB production processes illustrated in the '913, '999, '152 and'401 patents discussed above, and should be applicable in connectionwith all reactors and reactor systems that are used for the productionof highly reactive and/or mid-range vinylidene content PIB polymerproducts using liquid phase polymerization procedures. In this regard,it is to be noted that the feedstock for such reactors may compriseeither isobutylene or an admixture of isobutylene and a suitablenon-reactive diluent (solvent) therefor. Suitable feedstocks aredescribed generally in the '913, '999, '152 and '401 patents discussedabove. A particularly preferred feedstock comprises a high purityisobutylene monomer having a composition as set forth below in Table 2.

TABLE 2 Concentrations of individual components of Isobutylene streamComponent Weight % Methane 0.026 Ethane 0.0006 Propane 0.0024 Propylene0.027 Isobutane 0.064 N-butane 0.010 Butene-1 0.016 Isobutylene 99.84T-butene-2 0.010 C-butene-2 0.063 1,3 butadiene 0.007 C₅+ 0.007

In accordance with the concepts and principles of the invention, in theliquid phase production of polyisobutylene, an important and formerlyunknown relationship between diluent concentration and the alphavinylidene content of the product has been discovered. That is to say,in accordance with the concepts and principles of the invention, it hasbeen discovered that an increase in diluent concentration in thereaction admixture generally results in higher alpha position(vinylidene) double bonds concentration in the product. Moreover, in thesame manner, an increase in diluent concentration leads generally togreatly improved (narrower) polydispersity indices. In these regards,and in further accordance with the invention, the diluent content in thereaction admixture may be 50 weight % or less, may desirably be 30weight % or less, and may optimally be 10 weight % or less. Ideally thedesired diluent for isobutylene may be isobutane, However, in a moregeneral sense, the desirable diluent should simply be capable ofdissolving both isobutylene and polyisobutylene and should be inert tothe polymer forming reactions taking place in the reactor. In thislatter regard, a C₃- C₁₆ alkane or alkene, or a mixture of suchsubstances, may be used as the diluent. Desirably the diluent may be aC₃- C₁₆ 1-alkene such as, for example, butene-1. In another sense, thediluent may advantageously comprise a mixture of hydrocarbons such as,for example, C₄s and other light hydrocarbons.

As mentioned above, the processes of the present invention may generallyand suitably be used in connection with the equipment and processesdescribed in the '913, '999, '152 and '401 patents. However, for furtherclarity, the invention will be described here in connection with asimplified experimental reaction system 10 shown schematically in FIG.1.

With reference to FIG. 1, the experimental reaction system 10 maydesirably include a loop reactor 10, a recirculation pump 12, anisobutylene monomer inlet 14 which may include a pump 16, a diluentinlet 18 which also may include a diluent pump 20, an inlet 22 for thecatalyst complex (initiator), and chilling system 24 to remove the heatof the exothermic polymerization reaction. As shown, the loop reactor 10may include segments 10 a, 10 b and 10 c as well as a pipe 26 whichinterconnects segments 10 a and 10 c as shown and provides a place forconnection of pump 12. And as can be seen in FIG. 1, a chilling system24 for the system may desirably include cooling jackets 24 a, 24 b and24 c respectively for the reactor segments 10 a, 10 b and 10 c, achilling fluid inlet 28 and a chilling fluid outlet 30. In addition, thesystem may also include a feedstock inlet 32, where the isobutylenemonomer and a diluent are received and admixed for introduction into thereactor, and a product outlet 34 where the crude polymer product iswithdrawn from the system.

In operation, a reaction mixture comprising isobutylene, a diluent forthe isobutylene and a catalyst composition are recirculated by pump 12through reactor segments 10 a, 10 b and 10 c and pipe 26 while reactionconditions suitable for causing at least a portion of the isobutylene toundergo polymerization to form a polyisobutylene product includingpolyisobutylene molecules are maintained in the reactor 10. In themeanwhile, isobutylene and a diluent therefor are introduced into thereactor 10 via inlet 32, catalyst composition (initiator) is introducedinto the reactor via inlet 22 and crude product is withdrawn from thesystem via outlet 34.

Using the system 10, experiments were conducted maintaining the totalflow rate of monomer to the reactor loop at 100 mL/min. Reactions werecarried out at temperatures of 40° F. and 60° F. The pressure in thereactor loop was maintained at 200 psi. The internal diameter of thereactor tubes was 0.305″ and the total reactor volume was 228 cm³.Catalyst (initiator) flow was controlled at 0.02 mL/min such that thereaction set point was maintained. The recirculation rate in the reactorloop was 2 gpm. The catalyst composition comprised a complex of BF₃ andmethanol wherein the molar ratio of BF₃ to methanol was 1:1. No modifier(methanol) was added to the reactor separately from the catalystcomplex, although such a step might be desirable under some conditions.In this latter regard, the separate addition of modifier is described indetail in the '152 patent discussed above. A high purity isobutylene(purity>99.5 weight %) was used as the feedstock and a relatively highpurity isobutane (purity 95 to 98 weight %) was used as the diluent.

Experiments were conducted at various diluent concentration levels tostudy the effect of diluent concentration on alpha position double bondcontent, molecular weight (M_(N)) and polydispersity index (PDI) of theproduct. In these experiments, the diluent level was varied between 0and 27 weight %.

The chain end concentrations of the isomers were measured using ¹³C NMRspectroscopy. The molecular weight measurements were made using sizeexclusion chromatography (SEC).

The results of the experimentation are illustrated in FIGS. 2, 3 and 4.FIG. 2 shows variations in alpha position double bond isobutylene isomercontent with changes in isobutane diluent concentration at 40° F. And ascan be seen in FIG. 2, alpha isomer content increases with increaseddiluent concentration. Thus it is clear that the alpha isomer content ofthe product may be increased simply by increasing the concentration ofthe diluent in the reaction admixture. Also it is clear that if otherconditions dictate, the alpha isomer content of the product may bedecreased simply by decreasing the concentration of the diluent in thereaction admixture.

With reference to FIG. 3, the influence of diluent concentration onnumber average molecular weight (M_(N)) and polydispersity index (PDI)can be seen. In FIG. 3, M_(N) values are shown on the left axis and arerepresented by the filled symbols, while PDI values are shown on theright axis and are represented by the unfilled symbols. Of particularinterest is the large drop in PDI at almost constant molecular weightbetween 0 and 10 wt % of diluent (isobutane) concentration. This may beof particular benefit in meeting the commercially valuablepolydispersity specifications for PIB polymers. Thus it is clear thatthe PDI of the product may be decreased simply by increasing theconcentration of the diluent in the reaction admixture. Also it is clearthat if other conditions dictate, the PDI of the product may beincreased simply by decreasing the concentration of the diluent in thereaction admixture. Furthermore it is clear that the molecular weight ofthe product may be decreased simply by increasing the concentration ofthe diluent in the reaction admixture. Also it is clear that if otherconditions dictate, the molecular weight of the product may be increasedsimply by decreasing the concentration of the diluent in the reactionadmixture.

With reference to FIG. 4 it can also be seen that the rate of conversionof isobutylene into polyisobutylene increases with increasing diluentcontent. This perhaps can be attributed to the fact that higher diluentconcentrations in the reactor may provide improved heat transfercharacteristics.

As can be seen from the foregoing, alpha isomer content increases,polydispersity decreases, conversion increases and molecular weightdecreases with increasing isobutane diluent concentration. Trendssimilar to those observed at 40° F. were also observed when thepolymerization reactions were conducted at 60° F. Tabulated experimentaldata is reported below in Tables 3 and 4. As can be seen, these Tablesalso show the concentration of alpha and beta isomers in thepolyisobutylene product obtained.

TABLE 3 Data showing the effect of diluent concentration on PIBproperties at 40° F. Number Isobutane Average ConcentrationConcentration Diluent Molecular of Alpha of Beta Concentration WeightPolydispersity Isomer Isomer Other Conversion (wt %) (M_(N)) Index (PDI)(Structure I) (Structure IV) Isomers Rate 0 3318 3.81 54.2 NA NA 17.9 53288 3.31 56.5 33.6 9.9 22.1 10 3155 2.47 59.9 32.3 7.8 24.6 15 29092.25 65.4 32.5 2.1 27.2 20 2724 2.22 73.41 18.1 8.4 29.1 27 1785 2.1975.3 20.3 4.4 33.4

TABLE 4 Data showing the effect of diluent concentration on PIBproperties at 60° F. Number Isobutane Average Concentration DiluentMolecular of Alpha Concentration Concentration Weight PolydispersityIsomer of Beta Isomer Other Conversion (wt %) (M_(N)) Index (PDI)(Structure I) (Structure IV) Isomers Rate 0 2249 2.71 53.0 NA NA 48.3 52373 2.23 54.4 34.8 10.8  52.3 10 2217 2.17 63.1 30.7 6.2 51.5 15 16371.91 69.5 25.3 5.2 57.5 20 1389 1.89 70.0 22.9 7.1 57.7 27 1109 1.8573.3 17.6 9.1 62.3

In further accordance with the concepts and principles of the invention,the process also may provide for the continuous recycle of diluentand/or unreacted isobutylene. Such a process is depicted schematicallyin FIG. 5. With reference to FIG. 5, a reaction admixture comprisingisobutylene, a diluent for isobutylene (advantageously isobutane) and acatalyst composition (preferably a complex of BF₃ and a complexing agentsuch as methanol) is subjected in reactor 200 to reaction conditionssuitable for causing at least a portion of the isobutylene to undergopolymerization to form a polyisobutylene product includingpolyisobutylene molecules. The conditions in reactor 200 are such thatat least a fraction of the thus produced polyisobutylene molecules inthe product have alpha position double bonds and the polyisobutyleneproduct has a number average molecular weight and a polydispersityindex. Upon leaving the reactor 200 the crude polyisobutylene product iswashed in a scrubber 202 to remove catalyst residue and is subjected toflashing in a crude flash zone 204 to remove diluent and unreactedisobutylene. The product is then appropriately beneficiated further in aflash unit 212 and delivered downstream via outlet 24. At least aportion of the diluent and unreacted isobutylene flashed in zone 204 maythen desirably be continuously recycled overhead back to the reactor 200via lines 206 and 208. The diluent concentration in the reactionadmixture in reactor 200 may desirably be manipulated and/or keptconstant at any given time at such a level that it provides maximumbenefit to the process in maintaining a desired alpha isomer content aswell as in maintaining a low PDI. This, of course, may be done by addingdiluent via line 216. The feed rate of fresh isobutylene delivered vialine 210 may then be determined by the isobutylene conversion rate inthe reactor, i.e., the higher the conversion rate, the higher the rateof fresh isobutylene feed. In addition, whenever desired, the diluentconcentration may be varied to alter the alpha isomer content of theproduct, the PDI of the product, the molecular weight of the productand/or the conversion rate. In this latter connection, it is noteworthythat the alpha isomer content of the product and the conversion ratevary directly with diluent concentration while product molecular weightand PDI vary indirectly with diluent concentration.

Additional experimental data was gathered in connection with studiesinvolving the synthesis of a highly reactive grade (alpha double bondcontent more than 80%) PIB using a scaled up version of a reactor whichis set up essentially the same as the reactor 10. In connection withthese studies, additional modifier is introduced essentially asdescribed in the '152 patent. These studies reveal that it is greatlybeneficial to operate the reactor using an isobutane diluentconcentration of about 8-15 weight % and the following discussion isbased on data derived therefrom.

In these studies a reaction temperature of about 27° F. was maintainedemploying a chiller temperature of about 50° F. The input flow rate(isobutylene+diluent) was approximately 26 gpm and the volumetric flowrate of the recirculation pump was about 1260 gpm.

The catalyst flow rate was adjusted (ideally to between 0.03 and 0.05weight % of the feed rate) such that a constant operating temperaturewas maintained. As per the '152 patent, the modifier was introducedseparately into the reactor maintaining a methanol to catalyst ratio of0.63:1 to synthesize a highly reactive (high vinylidene content) PIBproduct. In a highly reactive product, it is desirable for the molecularweight (M_(N)), the PDI and the viscosity to be within certain limits,usually dictated by product specifications. One such product may havethe following specifications: M_(N)—2100 to 2500; PDI—1.6 to 2.2;Kinematic Viscosity (v)—1500 to 1750; and Alpha double bondcontent—Greater than 80 mole %. The usual aim of the manufacturingprocess is that all these specifications be met simultaneously.

In connection with the foregoing, the Kinematic viscosity (v) wasmeasured using Cannon Fenske tubes immersed in a viscosity bath (KoehlerKV3000). The M_(N) and PDI measurements were obtained using SECmeasurements as described earlier. The values obtained for the differentparameters are as shown in FIG. 6 thru 9. The dark heavy lines on thegraphs show the desired specification parameters.

An essentially pure isobutane stream having a composition as set forthin Table 5 below was obtained from ISGAS for use in an effort to isolatethe effects on PIB production of minor impurities in the isobutanediluent, although in a real practical sense it is generally not feasibleto use such a material in a commercial operation. The total oxygenatecontent of the pure diluent stream was less than about 5 ppm (≈3,4 ppmmethanol; ≈1.4 ppm MTBE).

TABLE 5 Purity of individual components of Isobutane diluent (99.8%purity) Components Weight % Propane 0.02 Isobutane 99.79 N-butane 0.18

The experimental set-up and conditions for these efforts wereessentially the same as those described above in connection withreaction system 10. The experimental data obtained as a result of theseefforts are set forth below in Table 6.

TABLE 6 Product properties obtained using high purity Isobutane Alphaposition Isobutane double diluent bond concentration Kinematic contentweight % M_(N) PDI Viscosity mole % 0 3292 4 3489 61.4 8 3197.7 2.552693 58.5 13 2946.9 2.48 2637 59.9 18 2883 2.43 2628 60.1 25 2751 2.292213 60.3

It can be observed from Table 6 that the major advantage of being ableto operate so as to produce a PIB having decreased polydispersity wasachieved. That is to say a substantial decrease in PDI andsimultaneously in viscosity is achieved with increasing diluentconcentration, while almost constant molecular weight is maintained.This is beneficial in a commercial sense for meeting both M_(N) andPDI/viscosity specifications simultaneously. However, there is almost nochange in the alpha double bond content with increasing isobutanediluent concentration as was observed in the case of lower purityisobutane.

In view of the foregoing it is clear that the present invention providesa mechanism for greatly reducing both PDI and viscosity by increasingdiluent concentration with no substantial corresponding decrease inmolecular weight. In addition, both viscosity and PDI can be maintainedwithin specifications while achieving a target molecular weight. This isespecially important in the production of HR (high vinylidene) grades ofPIB where controlling the polydispersity and viscosity withinspecifications is of paramount importance. Moreover, the use of a lowerpurity isobutane diluent resulted in higher alpha double bond content ascompared to high purity isobutane diluent. This could be the result ofthe presence of other hydrocarbon components in the feed or could be dueto the presence of oxygenates other than methanol. With regard to theforegoing, it seems to be more likely that the other oxygenates play arole in the increased vinylidene content. In accordance with ourstudies, the primary suspect is dimethyl ether. These oxygenates play arole similar to additional methanol that is added as a modifier. As isknown, methanol is also an oxygenate which may be added in a controlledmanner to regulate vinylidene content.

It appears that the invention provides the greatest benefit when the PIBproduction process is operated using a diluent concentration in therange of from about 8 to about 15 weight %, beyond which the gains arediminished as M_(N) starts to decrease, especially when a lower purity(industrial grade) isobutane diluent is employed.

Although alpha position double bond content increases with increasingisobutane dilution (in the impure isobutane example), the more desiredmanner to control alpha content by setting a suitable methanol tocatalyst ratio. This is due to the fact that there usually is minimalcontrol in an industrial setting over feedstock composition.

1. A process for production of polyisobutylene comprising: subjecting areaction admixture comprising isobutylene, a diluent for saidisobutylene and a catalyst composition to reaction conditions suitablefor causing at least a portion of said isobutylene to undergopolymerization to form a polyisobutylene product includingpolyisobutylene molecules, at least a fraction of said polyisobutylenemolecules having alpha position double bonds, said polyisobutyleneproduct having a number average molecular weight and a polydispersityindex; and manipulating the concentration of said diluent in saidadmixture to thereby control any one or more of (a) the relative size ofsaid fraction, (b) the number average molecular weight of said product,(c) the polydispersity index of said product and (d) the relative sizeof said portion.
 2. A process as set forth in claim 1, wherein saiddiluent comprises isobutane.
 3. A process as set forth in claim 1,wherein said catalyst composition comprises BF₃.
 4. A process as setforth in claim 1, wherein said catalyst composition comprises a complexof BF₃ and a complexing agent.
 5. A process as set forth in claim 4,wherein said complexing agent comprises a primary alcohol.
 6. A processas set forth in claim 5, wherein said complexing agent comprisesmethanol.
 7. A process as set forth in claim 1, wherein the relativesize of said fraction is a direct function of the diluent concentration.8. A process as set forth in claim 1, wherein the polydispersity indexis an indirect function of the diluent concentration.
 9. A process asset forth in claim 1, wherein the relative size of said portion is adirect function of the diluent concentration.
 10. A process as set forthin claim 1, wherein said reaction admixture is subjected to saidreaction conditions in a reaction zone where the reaction admixture ismaintained in an intimately intermixed condition.
 11. A process as setforth in claim 10, wherein said zone comprises a loop reactor reactionzone.
 12. A process as set forth in claim 1, comprising increasing theconcentration of said diluent in said admixture to thereby increase therelative size of said fraction.
 13. A process as set forth in claim 1,comprising decreasing the concentration of said diluent in saidadmixture to thereby increase the polydispersity index of said product.14. A process as set forth in claim 1, comprising increasing theconcentration of said diluent in said admixture to thereby increase therelative size of said portion.
 15. A process as set forth in claim 1,wherein the concentration of said diluent in said admixture is no morethan about 50%.
 16. A process as set forth in claim 1, wherein theconcentration of said diluent in said admixture is no more than about30%.
 17. A process as set forth in claim 6, wherein said reactionadmixture is subjected to said reaction conditions in a reaction zonewhere the reaction admixture is maintained in an intimately intermixedcondition.
 18. A process as set forth in claim 17, wherein said zonecomprises a loop reactor reaction zone.
 19. A process as set forth inclaim 17, wherein the concentration of said isobutane in said admixtureis no more than about 30%.
 20. A process as set forth in claim 1,further comprising selecting a diluent concentration for said admixturecorresponding to a given relative size of said fraction, saidmanipulating step comprising maintaining the diluent content of theadmixture at said selected concentration to thereby hold the relativesize of said fraction essentially constant.
 21. A process as set forthin claim 1, further comprising selecting a diluent concentration forsaid admixture corresponding to a given polydispersity index level, saidmanipulating step comprising maintaining the diluent content of theadmixture at said selected concentration to thereby hold thepolydispersity index of said product essentially constant.
 22. A processas set forth in claim 1, further comprising selecting a diluentconcentration for said admixture corresponding to a given relative sizeof said portion, said manipulating step comprising maintaining thediluent content of the admixture at said selected concentration tothereby hold the relative size of said portion essentially constant. 23.A process for production of polyisobutylene comprising: subjecting areaction admixture comprising isobutylene, a diluent for saidisobutylene and a catalyst composition to reaction conditions suitablefor causing at least a portion of said isobutylene to undergopolymerization to form a polyisobutylene product includingpolyisobutylene molecules, at least a fraction of said polyisobutylenemolecules having alpha position double bonds, said polyisobutyleneproduct having a number average molecular weight and a polydispersityindex, said polyisobutylene product having at least one parameter thatis variable as a function of the concentration of said diluent in saidadmixture, said at least one parameter comprising (a) the relative sizeof said fraction, (b) the number average molecular weight of saidproduct, (c) the polydispersity index of said product or (d) therelative size of said portion; choosing a diluent concentrationcorresponding to a pre-selected value of said at least one parameter;and maintaining the admixture at said chosen diluent concentration tothereby hold said parameter at said pre-selected value.
 24. A process asset forth in claim 23 wherein said at least one parameter comprises therelative size of said portion.
 25. A process as set forth in claim 23wherein said at least one parameter comprises the number averagemolecular weight of said product.
 25. A process as set forth in claim 23wherein said at least one parameter comprises the polydispersity indexof said product.
 26. A process as set forth in claim 23 wherein said atleast one parameter comprises the relative size of said fraction.
 27. Aprocess as set forth in claim 23, wherein said diluent comprisesisobutane.
 28. A process as set forth in claim 23, wherein said catalystcomposition comprises BF₃.
 29. A process as set forth in claim 23,wherein said catalyst composition comprises a complex of BF₃ and acomplexing agent.
 30. A process as set forth in claim 29, wherein saidcomplexing agent comprises a primary alcohol.
 31. A process as set forthin claim 30, wherein said complexing agent comprises methanol.
 32. In aprocess for production of polyisobutylene wherein a reaction admixtureincluding isobutylene, a diluent for said isobutylene and a catalystcomposition is subjected to reaction conditions suitable for causing atleast a portion of said isobutylene to undergo polymerization to form apolyisobutylene product including polyisobutylene molecules, wherein atleast a fraction of said polyisobutylene molecules have alpha positiondouble bonds and wherein said polyisobutylene product has a numberaverage molecular weight and a polydispersity index, the improvementcomprising increasing the concentration of the diluent in the admixtureto thereby increase the relative size of said fraction, increase therelative size of said portion, decrease the number average molecularweight of said product, or decrease the polydispersity index of saidproduct.
 33. In a process for production of polyisobutylene wherein areaction admixture including isobutylene, a diluent for said isobutyleneand a catalyst composition is subjected to reaction conditions suitablefor causing at least a portion of said isobutylene to undergopolymerization to form a polyisobutylene product includingpolyisobutylene molecules, wherein at least a fraction of saidpolyisobutylene molecules have alpha position double bonds and whereinsaid polyisobutylene product has a number average molecular weight and apolydispersity index, the improvement comprising decreasing theconcentration of the diluent in the admixture to thereby decrease therelative size of said fraction, decrease the relative size of saidportion, increase the number average molecular weight of said product,or increase the polydispersity index of said product.
 34. A process forproduction of polyisobutylene comprising: subjecting a reactionadmixture comprising isobutylene, a diluent for said isobutylene and acatalyst composition to reaction conditions in a reaction zone suitablefor causing at least a portion of said isobutylene to undergopolymerization to form a polyisobutylene product includingpolyisobutylene molecules, at least a fraction of said polyisobutylenemolecules having alpha position double bonds, said polyisobutyleneproduct having a number average molecular weight and a polydispersityindex, said polyisobutylene product having at least one parameter thatis variable as a function of the concentration of said diluent in saidadmixture, said at least one parameter comprising (a) the relative sizeof said fraction, (b) the number average molecular weight of saidproduct, (c) the polydispersity index of said product or (d) therelative size of said portion; choosing a diluent concentrationcorresponding to a pre-selected value of said at least one parameter;maintaining the admixture at said chosen diluent concentration tothereby hold said parameter at said pre-selected value; treating saidproduct to remove diluent and unreacted isobutylene therefrom; andrecycling at least one of the diluent and the unreacted isobutylene backto said zone.
 35. A polyisobutylene product produced by the process ofclaim
 1. 36. A polyisobutylene product produced by the process of claim6.
 37. A polyisobutylene product produced by the process of claim 12.38. A polyisobutylene product produced by the process of claim
 13. 39. Apolyisobutylene product produced by the process of claim
 20. 40. Apolyisobutylene product produced by the process of claim
 21. 41. Apolyisobutylene product produced by the process of claim
 23. 42. Apolyisobutylene product produced by the process of claim
 25. 43. Apolyisobutylene product produced by the process of claim
 26. 44. Apolyisobutylene product produced by the process of claim
 31. 45. Apolyisobutylene product produced by the process of claim
 32. 46. Apolyisobutylene product produced by the process of claim
 33. 47. Apolyisobutylene product produced by the process of claim
 34. 48. Aprocess as set forth in claim 1, 6, 12, 13, 20, 21, 23, 25, 26, 31, 32,33 or 34, wherein said diluent comprises a C₃-C₁₆ alkane or alkene, or amixture of such substances.
 49. A process as set forth in claim 48,wherein said diluent comprises a C₃-C₁₆ 1-alkene.
 50. A process as setforth in claim 48, wherein said diluent comprises isobutane.
 51. Apolyisobutylene product as set forth in claim 35, 36, 37, 38, 39, 40,41, 42, 43, 44, 45, 46 or 47, wherein the diluent comprises a C₃-C₁₆1-alkene.
 52. A polyisobutylene product as set forth in claim 51,wherein the diluent comprises a C₃-C₁₆ 1-alkene.
 53. A polyisobutyleneproduct as set forth in claim 51, wherein the diluent comprisesisobutane.